Conservation implications of change in antipredator behavior in fragmented habitat: Boreal rodent, the bank vole, as an experimental model

Biological Conservation 184 (2015) 11–17

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Conservation implications of change in antipredator behavior in fragmented habitat: Boreal rodent, the bank vole, as an experimental model Marko Haapakoski a,⇑, Janne Sundell b, Hannu Ylönen a a b

Department of Biological and Environmental Science, Konnevesi Research Station, University of Jyväskylä, PO Box 35, 40014 Jyväskylä, Finland Lammi Biological Station, University of Helsinki, Pääjärventie 320, 16900 Lammi, Finland

a r t i c l e

i n f o

Article history: Received 25 March 2014 Received in revised form 16 December 2014 Accepted 23 December 2014

Keywords: Myodes = Clethrionomys glareolus Predator prey interaction Breeding suppression Indirect predation Fear

a b s t r a c t Habitat fragmentation is known to cause population declines but the mechanisms leading to the decline are not fully understood. Fragmentation is likely to lead to changes in predation risk, which may cause behavioral responses with possible population level consequences. It has recently been shown that the awareness of predator presence, resulting in a fear response, strongly affects behavior and physiology of the prey individuals. Costs arising from fear may be as important for the prey population size as the direct killing of prey. We tested how predation risk in the form of scent of a specialist predator, the least weasel (Mustela nivalis nivalis), affects bank vole (Myodes glareolus) behavior in fragmented enclosures consisting of either non-fragmented (one patch) or fragmented (four patches) habitats of the same total area. Vole movement areas tended to be larger in the non-fragmented habitat. Fear decreased vole activity and tended to increase the use of the open matrix area. No interactions between fragmentation and fear treatments or differences in breeding related behaviors or fitness were found in our short-term experiment. However, behavioral mechanisms such as decreased activity and change of movements to the risky matrix could cause negative effects and population decline in the long run. Fragmentation is a serious issue in all human exploited habitats causing animals to face more risks compared to more uniform and sheltering environments. This should be especially taken into account in conservation of habitat and the reintroduction of captive reared animals where both intact sheltering habitats and food providing have habitats become rarer. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction Habitat loss and fragmentation are considered two of the main causes for declines in species richness and populations (MA, 2005). The main driver of declining populations is habitat loss, but habitat fragmentation, which subdivides populations into smaller units, may be an equally important factor affecting population trajectories (Lindenmayer and Fischer, 2006). However, we do not fully understand the individual and population level processes determining species persistence or explaining the observed declines in population size in fragmented habitats (Banks et al., 2007). During the mid-1990s, behavioral ecologists started to apply their knowledge of animal behavior to conservation biology. For example, Sutherland (1998) reviewed the role of behavioral ecology in conservation studies and concluded that behavioral

⇑ Corresponding author. E-mail address: marko.j.haapakoski@jyu.fi (M. Haapakoski). http://dx.doi.org/10.1016/j.biocon.2014.12.023 0006-3207/Ó 2015 Elsevier Ltd. All rights reserved.

aspects were largely neglected in previous conservation actions. Caro (2007) argued that behavioral ecologists have made little contribution to theory of conserving animal populations over the preceding decade. He suggested that behavioral ecology still has a lot to give to conservation and can provide practical solutions for reversing the decline of small populations. One area in which behavioral ecology has been able to contribute to conservation is the study of how habitat fragmentation can change the behavior of individuals (Fischer and Lindenmayer, 2007). Habitat fragmentation inevitably affects the behavior of an individual, such as, space use, social behavior and mate searching, which are all strongly linked to reproductive success (Ims et al., 1993; Björnstad et al., 1998; Andreassen et al., 1998; Haapakoski and Ylönen, 2010). These behavioral mechanisms may form an essential part of observed population declines (see review by Banks et al. (2007)). Habitat fragmentation affects movements of individuals between suitable habitat patches (Fahrig and Merriam, 1994). Dispersion of receptive females in the breeding

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habitat, the key resource for male reproductive success (Ims, 1988; Lin and Batzli, 2004), forces males to move more and to take more risks in a fragmented habitat compared to males in a sheltered closed habitat (Haapakoski and Ylönen, 2010). Preisser et al.’s (2005) meta-analysis started the discussion and research on the strength of negative population effects of predator intimidation. The mere risk of predation is known to be able to affect the behavior and physiology of prey (Lima and Dill, 1990; Lima, 1998a; Lima, 2002). Fear effects arise when a prey alters its behavior in response to predation risk, and these responses carry survival or reproductive costs (Boonstra et al., 1998; Preisser et al., 2005; Creel and Christianson, 2008). A common response of prey to predation risk is to avoid contacts with the predator by reducing activity or by escaping (Sundell and Ylönen, 2004; Mäkelainen et al., 2014). Reduced activity will often lead to a reduction in foraging and consequently may decrease the condition of an individual (Creel and Christianson, 2008). Poor body condition can cause decreased immune function, which increases susceptibility to parasites and pathogens. This may lead to a vicious circle where an already poor body condition is decreased even more due to parasites and pathogens (Beldomenico et al., 2008). In addition, predator avoidance causing a decrease in activity during the mating season may lead to missed encounters with potential mates (Brown, 1988) and hence to lower fitness. In females, poor body condition can diminish breeding success in terms of offspring numbers and/or quality (Lindström, 1999). In the so called breeding suppression hypothesis, Ylönen and Ronkainen (1994) proposed that by suppressing or delaying breeding under predation risk, prey females can enhance their lifetime reproductive success. However, Kokko and Ranta’s (1996) modeling study suggested that suppression of breeding under predation risk is not an optimal strategy, however, the delay or reduction of reproduction could still be significant (Haapakoski et al. 2012). Also songbirds with a manipulated risk of weasel visits in nest cavities had a strong negative response in reproductive effort (Mönkkönen et al., 2009), and in the experiment by Zanette et al. (2011), mere predator bird sound playback decreased the bird offspring numbers by 40%. Habitat fragmentation has the potential to change the interactions between species. One important example of this is predator–prey-interaction, which can change due to habitat fragmentation (Ryall and Fahrig, 2006). Fear is not evenly spread in the landscape and a prey experiences a different level of fear in different parts of its area of use (for review see Laundré et al., 2010). Creel et al. (2005) showed that elk (Cervus elaphus) avoided predation by wolves (Canis lupus) by moving to poorer woody habitat from rich grassy habitat. The change in spatial pattern of elk herbivory increased plant growth rates in riparian areas that elk avoided to minimize risk of predation (Ripple and Beschta, 2007). Fear effects and prey habitat shifts are not limited to terrestrial habitat. Wirsing et al. (2008) showed sublethal effects of predatory sharks and whales on bottlenose dolphins (Tursiops sp.), harbor seals (Phoca vitulina), and dugongs (Dugong dugon). In each case, foraging individuals spent less time in more profitable but risky patches or decreased their use of risky feeding tactics that would increase net energy gain. Experimental evidence has also shown that predation risk can shape spatial and temporal patterns of prey resource and have a pivotal role in determining the small-scale distribution patterns of rocky intertidal foundation species (Matassa and Trussell, 2011). The same life history parameters that change due to fragmentation (Banks et al., 2007), such as mortality and reproduction, are also suggested to change under the effect of fear. Creel and Christianson (2008) proposed that there is a need to understand the effect of fear in conservation biology and management, since this field of science traditionally takes only direct predation into

account. They also pointed out that risk effects can be wrongly interpreted to be consequences of limited food supply, especially in the cases where fear effects reduce reproduction rather than survival. The impact of predators is mediated by the amount and configuration of risky habitat. Suggesting that quantifying the landscape of fear could be a useful tool in the management and conservation of wildlife populations (Laundré et al., 2010). As endangered species or ecosystems are such that they do not allow experimentation, manipulation of landscape or individual properties, it is important to have appropriate experimental model systems (e.g. Ims and Andreassen, 1999) to accumulate knowledge needed for conservation issues in systems and species more difficult to study (Ims et al., 1993). The bank vole (Myodes glareolus) is an ideal study species to gain insight into the conservation implications of fear. There is a large body of background literature available on the basic ecology, behavior of the species as well as the effects of fragmentation on the species (Haapakoski and Ylönen, 2010, 2013). In addition, the bank vole is a very abundant species, which allows experimentation in a way not possible for endangered species due to ethical considerations. In this experiment we tested whether increased fear, caused by the presence of the scent of a specialist predator, the least weasel (Mustela nivalis nivalis) in combination with habitat fragmentation is affecting bank vole spacing behavior and survival. We predicted that (1) fear of a specialist predator inside habitat patches drives voles out from safe habitat into the matrix and therefore possibly into the talons of owls and raptors. This process, called predator facilitation (Kotler et al., 2004), should be stronger in fragmented habitat. (2) Antipredator behavior caused by the fear could result in reduced activity and movements (Lima and Dill, 1990) leading to missed mating opportunities and delayed breeding under increased risk of predation (Ylönen and Ronkainen, 1994; Haapakoski et al. 2012).

2. Material and methods 2.1. Study site and experimental set-up The experiment was conducted at the Konnevesi Research Station of the University of Jyväskylä in Central Finland (N62°, E26°). Six outdoor enclosures, 50 m  50 m (0.25 ha), made of galvanized steel sheets were used in this experiment. Enclosures were built on an old agricultural field that was ploughed and sown with a meadow grass seed mixture to produce similar vegetation in all enclosures. The fence reached about 0.75 m above the ground and 0.5 m into the ground. Enclosures prevented experimental animals from escaping and small mammalian predators from entering the enclosures. Enclosures were not covered and avian predators had free access to enclosures. The habitat of the enclosures was manipulated by forming either one large (non-fragmented) or four small habitat patches (fragmented) with a total habitat area of 900 m2 in each enclosure (Fig. 1). Habitat patches consisted of thick tall grass of approximately 0.5–1.0 m height of Phleum, Festuca and Deschampsia grasses with some Chamerion, Anthriscus sylvestris and Urtica dioica. In the matrix area surrounding the patch(es), vegetation was kept low by regular removal and the re-growth was prevented with the herbicide Round-UpÒ, thus the vegetation was absent or very low and sparse (0–10 cm). In the fragmented enclosures there were 25 Ugglan traps (Ugglan special, Grahnab ab, Hillerstorp, Sweden) and in non-fragmented enclosures 24 traps per enclosure arranged so that 16 traps were always inside the tall grass habitat and nine or eight traps in the open matrix (Fig. 1). The traps were placed in the habitat patches in a grid at intervals of about 8 m (Fig. 1) and were covered with metal trap chimneys of 40  40  50 cm3 in size. Traps on the

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Fig. 1. Layout of experimental enclosures: non-fragmented enclosure with one large habitat patch and fragmented enclosure with four small habitat patches, three of both types of enclosures were used in the experiment. Grey represents habitat area, white matrix area and small black squares indicate trap locations. Numbers show the size in meters.

matrix were covered by 25 cm  15 cm wooden plates. Chimneys and wood plates protected trapped voles from direct sunlight and rain.

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were trapped next to the research station and released back to the same place after each experimental round. After trapping, mice were kept singly in large rodent cages (38  59  19 cm3) with wood shavings and hay as bedding. Rodent food pellets, sun flower seeds and fresh water were available ad libitum. Safe habitat for voles is also a safe and preferred habitat for mice and weasels (Haapakoski et al., 2013). All the small mammals in this experiment share the same avian predators and are most vulnerable in the matrix which does not provide shelter or any other resources for them. This leads to mice and weasel leaving their scent marks inside safe habitat and leaving only the matrix habitat unmarked. The study voles were marked individually with ear tags (Hasco Tag Company, Dayton Kentucky U.S.A, tag No. 1005-1). The age, weight and lab/enclosure-born individual voles were distributed in the enclosures as evenly as possible, and relatives were not placed in the same enclosure. Weasels and mice were marked with light 1.8 g (3% weight of weasels and 5% of mice) radio-collars (Biotrack, Wareham, UK). Radio-collars were attached one day before release of weasels and mice into enclosures and removed immediately after recapture.

2.2. Study species and experimental animals 2.3. Enclosure experiment The bank vole is a common rodent inhabiting a wide geographical range in the Palearctic (Macdonald, 2001). Females are territorial during the breeding season and owning a territory is a necessity for female maturation and breeding (Kalela, 1957; Bujalska, 1973; Ylönen et al., 1988). Female home ranges are smaller than male home ranges which extend over several female home ranges (Bondrup-Nielsen and Karlsson, 1985). The size of the habitat patches in the fragmented treatment has been chosen so that at least four females were able to breed (Haapakoski and Ylönen, 2010, 2013). The distribution of females in breeding condition affect spacing and movements of males (Ims, 1987) and previous studies have shown that one male is able to visit all habitat patches (Haapakoski and Ylönen, 2010, 2013). Our experimental vole density of 32 females/ha represents a natural situation during increasing and peak densities for the study species (Ylönen et al., 1988, 1990). Voles used in the experiment were individuals of the first or the second laboratory-born generations of wild trapped individuals or the first generation individuals born in the outdoor enclosures during early summer. Prior to the experiment, the voles were housed individually in standard laboratory rodent cages (43  26  15 cm3). Cages had wood shavings and hay as bedding. Rodent food pellets and fresh water were available ad libitum. Voles were maintained under standard conditions (18 h light: 6 h dark; 20 °C), thus the laboratory conditions corresponded roughly to the natural light–dark regime during the field experiment. The least weasel is a small mustelid specialized on hunting small mammals. Population numbers of bank voles, like other small vole species, fluctuate cyclically in boreal landscapes (e.g. Hanski et al., 2001), and weasel populations follow the vole cycles with an approximately half-year time lag (Korpimäki et al., 1991). Six male weasels were used in this experiment. Prior to the experiments, weasels were housed singly in 60  80  60 cm3 cages in an outdoor shelter at the Konnevesi Research Station. Each cage had a nest box and bedding was provided in the form of wood shavings and hay. Weasels were fed daily with voles or chicken. As a non-predator control, yellow-necked mice (Apodemus flavicollis) were used. Yellow-necked mice are somewhat smaller to the weasel, but the species are comparable in their movement capabilities. Yellow-necked mice mark their territory with smelly urine marks in a similar manner to small mustelids (Macdonald, 2001). Yellow-necked mice also use a similar type of habitat as bank voles (Bujalska and Gruem, 2008). Mice for the experiment

On the first day, eight females were released into each enclosure (see experimental schedule from Table 1) where they were allowed to settle down and establish their own territories. In the evening of day 3, traps were baited with a mix of oat and sunflower seeds and were set to capture females back to the laboratory. Traps were checked in the mornings around 8 a.m. and in the evenings around 8 p.m. In the laboratory, females were placed into the same cages where they were living before release into the field. Female trappability was high and all females alive were returned to the laboratory before predation risk treatments began. The remains of the bait were always removed from the traps when the traps were not in use. In the evening of day 5, predation risk treatments in the form of weasels and yellow-necked mice as a non-predator control were released into different pairs of the fragmented and non-fragmented enclosures. A pair of fragmented and non-fragmented enclosures served as a control without any treatment. On day 7, after two days in the enclosures, weasels and mice were located using radio-tracking. After that weasels and mice were surrounded with traps and removed from the enclosure leaving only the scent behind. In the morning of day 8, bank vole females (missing females were replaced with new ones) were released back to the same trap sites from which they had been previously captured and returned to the laboratory. In addition, two males per enclosure were released one by one into random opposite corners of the habitat patch/es. In the evening of day 9, traps were set for assessing their movement area. This time traps were checked three times per day, approximately every eight hours for three days. When trapped, the animal location was recorded and it was released next to the trap. Beginning on day 12, voles were trapped for removal to the laboratory. The experiment was repeated three times with starting days of 6th of June, 27th of June and 18th of July, so that all the three enclosure pairs were used in each treatment with new voles for each run. In the laboratory, female cages were checked for new-born pups every morning. After birth, the litters were weighed and the number of pups for each litter was counted. When pups were 20 days old, they were separated from the mother and their sex was determined. We used the trapping data to analyze movement areas and the habitat patch content of the movement area for each male and female with Ranges VI program (Anatrack Ltd. Wareham, UK). The movement area was calculated with a 100% convex polygon. Trappability was calculated as a proportion of captures of each vole

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Table 1 Schedule of the experiment: Experiment was repeated with the same design three times during the summer starting 6th of June, 27th of June and 18th of July. Six enclosures were used so that each enclosure was used once in each predation risk treatment.

3.1. Activity The best model for activity included only the predation treatment (GLMM, predation: F2.10 = 3.8, p = 0.059) and Tukey post hoc tests showed that the fear of weasels decreased activity compared to the control treatment (weasel vs. control Z = 2.7, P = 0.017, weasel vs. mouse Z = 1.1, P = 0.487 and mouse vs. control Z = 1.6, P = 0.234, Fig. 2). 3.2. Vole movement areas The best model for the vole movement area included fragmentation and number of captures. Higher number of captures increased movement area and movement areas tended to be larger in the non-fragmented treatment (GLMM, fragmentation: F1,4 = 3.3, P = 0.143, GLMM, number of captures: F1,133 = 4.6, P = 0.033, Fig. 3). The best model for habitat patch content of the movement area included only predation risk (GLMM, predation: F2,10 = 2.9, P = 0.098). Tukey post hoc analysis revealed that the weasel treatment increased the proportion of matrix area in the total vole movement area compared to the control treatment (weasel vs. control Z = 2.4, P = 0.039, weasel vs. mouse Z = 1.0, P = 0.550 and mouse vs. control Z = 1.4, P = 0.335, Fig. 4). 3.3. Survival Survival of the voles was high (98.7 ± 1% in fragmented and 93.6 ± 3% in non-fragmented treatment) and the best model in

a

80

a 70

b

b 60

on tr ol M ou se W ea se l

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ea se l W

se

50 ou

Statistical analyses were conducted with R (R Development Core Team, 2010). Mixed effects models were fitted using library nlme (Pinheiro et al., 2010) and lme4 (Bates et al., 2010). Model selection was done by choosing the best model from the set of predefined models based on the lowest AIC value (see all models from electronic Supplementary material). The maximum likelihood method was used for fitting the models and restricted maximum likelihood (REML) in the final model to obtain the model parameter estimates. To account for pseudoreplication caused by 10 voles living in the same enclosure, enclosure within replicate was used as a random factor in all analyses (Crawley, 2007). Fragmentation (non-fragmented and fragmented), predation risk (control, mouse and weasel) and sex (female and male) were used as factors in all analyses. Vole activity (trappability) and habitat content of the movement area was analyzed with lme. Fragmentation ⁄ predation risk interaction with main effect of sex was used as a fixed factor, and vole individual within enclosures within replicate, as a random factor in the full model. In the movement area analysis the number of voles trapped was used as a covariate as well. Survival was analyzed with lmer using binary survival as a response variable. Fragmentation ⁄ predation risk interaction with main effect of sex was used as a fixed factor and vole individual within enclosures within replicate as a random factor in the full model with binary family and with logit link function. When analyzing reproductive output, only females were used. The proportion of breeding females was analyzed with lmer using the ‘‘breeding or not breeding’’ as a binary response variable. Fragmentation ⁄ predation risk interaction was used as a fixed factor and vole individual within enclosures within replicate as a random factor with binary family and with logit link function in the full model. Litter birth date, litter size and litter weight was analyzed with lme, in which fragmentation ⁄ predation risk interaction was used as fixed factor and vole individual within enclosures within replicate as a random factor in the full model. To check the assumptions of models, the normality of residuals and homogeneity of variance of the best models were plotted in R. This was done with each level of the random effects as well as with diagnostic plots (qqnorm in R). Possible autocorrelation of the residuals was checked with ACF plots in R. Multicollinearity was studied with a correlation matrix and with VIF. There was no indication of multicollinearity between covariates or autocorrelation in

3. Results

ro l

2.4. Statistical analyses

residuals. Tukey post hoc test were used for between treatments comparison.

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of the total number of trap checks during movement area trapping. We use trappability as a measure of vole activity in a similar manner as previous studies (Krebs and Boonstra, 1984; Gilbert et al., 1986; Ylönen et al., 1990). Because trappability differed between the treatments, the number of captures was used as a covariate in the movement analysis. Habitat content of the movement area was the percentage of habitat patch area within total movement area.

on t

7 8 9 12 26

Experimental steps Release of 8 females into each enclosure Removal of the females back to laboratory Release of the weasels for predation risk treatment and yellow necked mice as a novel control treatment into pairs of enclosures with fragmented or nonfragmented treatment Removal of weasels and yellow necked mice Releasing females into same location where they were captured and release of two males into each enclosure Starting of movement area trapping. Traps were checked three times per day End of movement area trapping and removal of voles back to laboratory First deliveries and weighing of pups in the laboratory

Trappability (%)

1 4 5

C

Day

Non-fragmented

Fragmented

Fig. 2. Activity of voles after treatment measured as trappability. Different letters indicate significant differences among the means after Tukey’s test (P < 0.05). Error bars denote standard error of the mean.

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the dataset. There was no difference in litter weight nor litter size between our treatments, and the null models were the best in both cases Table 2).

Movement area (m 2)

250 200 150

4. Discussion 100 50

Non-fragmented

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0

Fragmented

Fig. 3. Movement areas of voles in fragmented and non-fragmented habitat. Both sexes and predation risk treatment combined. Error bars denote standard error of the mean.

a

Habita area (%) of movement area

1.0

a 4.1. Antipredator behavior and movements

b

b

0.9

0.8

Non-fragmented

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W

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0.7

C

Fear of a specialist predator decreased voles’ activity and directed their decreased movements out of the safe habitat. In our study this was the case in both habitat fragmentation treatments, though voles tended to move over a larger area in the non-fragmented treatment. Specialist predators, such as the least weasel, seem to have a similar effect on prey behavior regardless of habitat configuration. Behavioral effects of our study support ideas proposed by Preisser et al. (2005) about a negative effect of intimidation. In our study, matrix around habitat patch/es with higher avian predation risk in the open matrix surrounding the shelter providing habitat patches, increased the intimidation effect. Fear of weasel teeth may drive voles to talons of raptors and owls (Kotler et al., 1992).

Fragmented

Fig. 4. Habitat content of the vole movement area counted from movement area based on the trapping data. Different letters indicate significant differences among the means after Tukey’s test (P < 0.05). Error bars denote standard error of the mean.

the survival analysis included only fragmentation (GLMM, fragmentation: v21,5 = 2.2, P = 0.133).

3.4. Recruitment There were no differences in the proportion of breeding females (null model the best: control 26.4 ± 8%, mouse 26.8 ± 7% and weasel 31.3 ± 7%). The best model for the date the litter was born was the full model showing a clear trend in the interaction between fragmentation and predation risk. Predation risk delayed the date when a litter was born, but only in fragmented enclosures whilst in non-fragmented enclosures there were no such patterns (GLMM, fragmentation ⁄ predation: F2,6 = 4.1, P = 0.074 Table 2.). However, predation risk effect was not significant when fragmentation treatments were analyzed separately (non-fragmented, GLMM, predation: F2,3 = 2.8, P = 0.205, fragmented, GLMM, predation: F2,3 = 1.2, P = 0.412), probably due to low power after splitting

Predation risk alone, mediated by indirect cues of predator presence, has been recognized as an important factor to negatively affect behavior and consequently also population processes (for review see Creel and Christianson, 2008). A common response of a prey under predation risk is to avoid contacts with the predator by reducing activity or movement areas (Lima, 1998b; Bolbroe et al., 2000). This was true also in our experiment where voles had the lowest trappability under weasel risk. We suggest that decreased activity lead to lower trappability, because trappability has commonly been used as a measure of activity in small rodent studies (Krebs and Boonstra, 1984; Gilbert et al., 1986; Ylönen et al., 1990). Trappability around 70%, like in our control enclosures, can be considered normal for bank voles, whilst less than 58% trappability, as observed here in the predation treatment, is one of the poorest in our enclosure studies with bank voles (Haapakoski and Ylönen, 2010, 2013). Regardless of decreased activity under fear, voles did not decrease their total movement area. It appears that voles in the enclosures directed their movements away from the safe habitat into the matrix, which increased their movement areas into the same level than in their conspecific in the control enclosures. Another antipredator response of voles was a microhabitat shift from the grassy habitat into the matrix. This phenomenon is called predator facilitation (Kotler et al., 1992) which states that prey living preferentially under cover are forced out of the safe habitat to open habitat by predators hunting in covered habitat. In our case voles escaped the risk of the specialist mammalian predator by moving into the matrix where they were more prone to get eaten by avian predators. Voles seemed to respond more to the most dangerous predator, or the scent of weasel in this case, as suggested by Relyea (2003). Our result was similar to the laboratory experiment of Korpimäki et al. (1996) in which field voles (Microtus agrestis) shifted their preference from long grass to short grass

Table 2 Female reproduction in the laboratory. The first row shows the day the litter was born (days after males release in the enclosure). The second row the mean number of pups born per pregnant female and the weight of the litter after delivery. Values are means and errors denote ± standard error.

Litters born (days after release of males) Number of pups/litter Litter weight (g)

Non-fragmented control

Non-fragmented mouse

Non-fragmented Weasel

Fragmented control

Fragmented mouse

Fragmented weasel

21.4 ± 1.1

19.2 ± 0.2

20.1 ± 0.4

19.0 ± 0.7

20.2 ± 0.6

21.0 ± 0.6

4.0 ± 0.6 7.0 ± 1.1

4.4 ± 0.6 7.6 ± 0.9

5.3 ± 0.4 9.7 ± 0.7

5.5 ± 0.6 8.9 ± 0.3

5.3 ± 0.8 8.7 ± 1.1

4.7 ± 0.6 8.2 ± 1.1

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under weasel predation risk, when there were no avian predators present. This response makes sense because in the matrix, weasels would also be at risk to become prey to avian predators (Haapakoski et al., 2013). However, in our experiment the weasel was not present anymore which makes the voles’ decision maladaptive in the long run. On the other hand, our voles should be able to estimate the avian predation risk (Kotler et al., 1992; Abramsky et al., 1996), which was constant across the landscape during our experiment. Moving of the voles to the matrix had no survival effect. Regardless of fragmentation and predation risk treatment, vole survival in the enclosures was high, around 95%, compared to around 80% (around 70% in the autumn) survival in the following year (Haapakoski et al., 2013). High survival during this experiment was most likely due to increasing vole densities outside enclosures providing plenty of food for birds of prey (Kallio et al., 2009). 4.2. Habitat fragmentation and predator avoidance Habitat fragmentation is a serious issue in all human exploited habitats causing animals to face more risks compared to more uniform and sheltering environments. Predation risk mediated only by an indirect cue left by a predator but without predator presence inside a protective or favored prey habitat has not been studied much (Korpimäki et al., 1996). Voles’ antipredator behavior was similar in both habitat fragmentation treatments. The most important effect concerning fragmentation is that voles moved more in the matrix area under predation risk regardless of fragmentation type. Similarly, elk moved to poor woody habitat from richer grassland when wolves are present (Creel et al., 2005). In our experiment and at this scale, it seems that the matrix is equally risky in both habitat fragmentation treatments, but still a better option than staying inside habitat with an increased cue of predation risk, fear. In other words, if one patch is surrounded by the matrix it may be similarly risky to many patches surrounded with matrix with the same habitat area, in the short-term (Haapakoski and Ylönen, 2010). This should be taken into account in conservation issues and reintroduction of captive reared animals in cases where both sheltering habitats and food providing habitats become rarer. In the macroecological scale our result may explain unimodal pattern linking species richness in heterogeneous landscapes (Allouche et al., 2012). According area–heterogeneity and species diversity tradeoff theory increasing landscape heterogeneity along increased fragmentation may increase available niches for species until a threshold, where the quality of each species specific niche decreases. This decrease after threshold might be explained by higher exposure to predation in the matrix around suitable patches. Vole movement areas and responses to the predation risk were similar regardless of sex of the voles and the habitat fragmentation treatment. The only clear trend was that movement areas tended to be larger in non-fragmented enclosures similarly as observed by Haapakoski et al. (2015). This suggest that individuals are responding with the so called fusion reaction (Ims et al., 1993), a common response in bank vole females (Haapakoski and Ylönen, 2010, 2015) in which an individual accepts to stay only in one patch and reduces its home range area. This is contrary to the fission reaction where individuals enlarge their movement areas by moving between separated habitat patches, which is typical for males in fragmented habitat (Diffendorfer et al., 1995; Andreassen et al., 1998; Haapakoski and Ylönen, 2010). In this experiment female density was high and male density low. Probably males’ high encounter rate with females decreased the male movement areas, because males did not need to move much when searching for females (Ims, 1988; Ylönen and Mappes, 1995). In the other experiments, males have usually moved over larger areas

including several patches in the fragmented habitat (Andreassen et al., 1998; Haapakoski and Ylönen, 2010; Haapakoski et al., 2015). 4.3. Fear effects on reproduction Decreased activity under predation risk during the reproductive period may lead to missed encounters with potential mates (Brown, 1988) or otherwise disturb sexual encounters (Ronkainen and Ylönen, 1994), although we could not detect this in our experiment. It seems that the best strategy for small short-lived animals is to attempt to reproduce during the best breeding season regardless of the predation risk (Trebaticka et al., 2012). Predation risk may well decrease or delay reproduction when combined with fear or some other limiting factor, for example food constraint at first reproduction after a long winter (Haapakoski et al., 2012) or high conspecific density during the late breeding season (Haapakoski et al., 2012; Jochym and Halle, 2012). Before the experiment, the yellow-necked mouse was regarded as being harmless for voles. However, our result that bank voles responded to the yellow-necked mice odor similarly, but not as strongly as to predator odor, suggests that there may be competition and interference between these rodent species rather than just peaceful habitat sharing (Bujalska and Gruem, 2008). Aggressive behavior has been observed between yellow-necked mice and bank voles with yellow-necked mice being dominant in encounters (Andrzejewski and Olszewski, 1963). Arboreal yellow-necked mice have been regarded as nest predators of hole-nesting passerines (Weidinger, 2002) and may therefore act as nest predators of sympatric rodents as well. This may be supported by our results that the bank vole tried to avoid encounters with yellow necked mice. 5. Conclusion Our experimental study brings new information about the possible mechanisms leading to population declines or local extinctions in fragmented multi-predator habitats. We have shown that fear of predation by a specialist mammalian predator may drive prey out of otherwise safe covered habitat into the risky open habitat, where the possibility of predation by avian predators is higher regardless of fragmentation type. This is likely to increase mortality when predation pressure is high in both habitats. In multi-predator systems with patchy landscapes, like most ecological systems are, predator facilitation should be taken into account when considering species persistence in the long term. Acknowledgements We thank field helpers, H. Jurkkala, K. Juutilainen and L. Trebaticka. Technicians of the Research Station helped maintain the enclosures. John Loehr made valuable comments on the language and the manuscript. The study was supported by the Finnish Academy. The Authors declare that there is no conflict of interest. Experiment was conducted with animal experimentation permission at Jyväskylä University No. 35/31.5.2004. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.biocon.2014.12. 023. References Abramsky, Z., Strauss, E., Subach, A., Riechman, A., Kotler, B., 1996. The effect of barn owls (Tyto alba) on the activity and microhabitat selection of Gerbillus allenbyi and G. pyramidum. Oecologia 105, 313–319.

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